This invention relates to a colour pickup tube containing a stripe type filter, and more particularly to an optical system utilized in the light receiving portion of such a pickup tube.
As is well known in the art, the optical system utilized in the light receiving portion at one end of such pickup tube, that is a single tube type colour pickup tube is constructed as follows. Thus, it generally includes an optical low pass filter, a colour compensating filter, a black mask, a stripe filter, a transparent electroconductive film, and a photoconductive film which are disposed in the order mentioned in a direction from an object toward the tube, and incorporated into the light receiving end of the tube. The term "optical low pass filter" is used herein to mean a filter which eliminates the high frequency components of the spatial frequencies of light, and typically comprises a quartz lens utilizing a double refraction phenomenon or a lenticular lens. The purpose of this filter is to prevent erroneous colouring of the picked up image. Such filter is effective to prevent erroneous colouring of the picked up image which occurs when the pitch of the high frequency components of the spatial frequencies of the light emanated by the object corresponds to the inherent pitch of the stripe filter. However, such filter is optically directive so that it is necessary to align the directivities of the filter and stripe filter when assembling them.
Various component elements described above of the optical system provided for the light receiving end of a pickup tube have been separately mounted on the light receiving end of the tube. However, as such method of independently and separately mounting the component elements is not advantageous from the standpoint of the characteristics and fabrication of the pickup tube, various improvements have been proposed. But even with such improvements, the following problems have not yet been solved. More particularly, since various component elements are separately and independently mounted, the optical interfaces of respective component elements act independently upon the incident light to the pickup tube with the result that the incident light is subjected to such optical actions as reflection, refraction and so forth at the interfaces of respective component elements.
Considering reflection for example, the incident light is reflected two times, one occurring at the time of incidence to an element, and the other at the time of issuing from the element. The loss of the incident light quantity caused by such reflections of course deteriorates the sensitivity and picture quality of the pickup tube. From the standpoint of fabrication, the method of independently and separately mounting respective component elements requires independent supports for respective elements which make it difficult to miniaturize the construction of the tube and to decrease the number of steps of fabrication and hence the cost of the tube. Further, the method of independent and separate mounting makes it possible to properly adjust the optical system. For example, where the optical low pass filter is made of quartz considerable difficulty is encountered for mounting the low pass filter with the crystal axis of the qualtz oriented at a predetermined angle with respect to the direction of the stripe filter. Further, it is also difficult to make parallel respective elements. Although such difficulties can be avoided by precisely designing and machining of the supports for the component element such measure increases the cost of manufacturing. Increases in the time and labour for mounting and adjustment increase not only the cost but also the chance of contaminating the photoconductive film due to deposition of dust or other foreign substances thus degrading the characteristic of the resulting tube. Thus, the prior method of independently manufacturing, storing, conveying, assembling and adjusting various component elements of the optical system increases the chance of contamination and damage of the optical surfaces of the elements, so that it is difficult to expect satisfactory results.